In recent years, various portable electronic devices have been spreading due to rapid development of techniques for downsizing electronic devices. Batteries as power sources for these portable electronic devices are also required to have a reduced size, and nonaqueous electrolyte secondary batteries having a high energy density receive attention.
Particularly, attempts have been made to use elements that form an alloy with lithium, such as silicon and tin, and substances having a large lithium absorption capacity and a high density, such as amorphous chalcogen compounds. Above all, silicon can absorb lithium up to 4.4 lithium atoms per silicon atom. Accordingly, when silicon is used as a negative electrode material of a nonaqueous electrolyte secondary battery, the negative electrode capacity per mass is about 10 times as large as that when conventional graphitic carbon is used as a negative electrode material. However, silicon significantly changes its volume as lithium is inserted and removed in a charge-discharge cycle, and thus there is a problem in cycle characteristics which is associated with micronization of active material particles, etc.
For solving the above-mentioned problem, attempts have been made to attain a high capacity and improve cycle characteristics by using an active material in which silicon-containing particles are combined with a carbonaceous substance. However, even with such an active material, both a high capacity and cycle characteristics are not sufficiently maintained, and it is required to more satisfactorily maintain both a high capacity and cycle characteristics and improve a capacity and cycle characteristics.